1. Field of the Invention
The present invention relates to a valve timing control device and is particular to a valve timing control device for controlling an angular phase difference between a crank shaft of a combustion engine and a cam shaft of the combustion engine.
2. Description of the Prior Art
In general, a valve timing of a combustion engine is determined by valve mechanisms driven by a cam shaft according to a characteristic of the combustion engine or the use of the combustion engine. Since a condition of the combustion may change in response to the rotational speed of the combustion engine, however, it is difficult to obtain an optimum valve timing through the whole rotational range. Therefore, in recent years, a valve timing control device which is able to change a valve timing in response to the condition of the combustion engine has been proposed as an auxiliary mechanism of the valve mechanism.
A conventional device of this kind is disclosed, for example, in U.S. Pat. No. 4,858,572. This device includes a rotor fixed on the cam shaft, a drive member driven by the rotational torque from a crank shaft and which rotatably mounted on the cam shaft so as to surround the rotor, a plurality of chambers that are defined between the drive member and the rotor and that each has a pair of circumferentially opposed walls and a plurality of vanes that are mounted to the rotor and extend outwardly therefrom in the radial direction into the chambers so as to divide each of the chambers into a first pressure chamber and a second pressure chamber. In this device, a fluid under pressure is supplied to a selected one of the first pressure chamber and the second pressure chamber in response to the running condition of the combustion engine and an angular phase difference between the crank shaft and the cam shaft is controlled so as to advance or retard the valve timing relative to the crank shaft. The valve timing control device is in the position of the maximum advanced condition, when each of the vanes contacts with one of the opposed walls of each of the chambers. On the other hand, the valve timing control device is in the position of the maximum retarded condition, when each of vanes contacts with the other of the opposed walls of each of the chambers.
In the above prior art device, if the fluid which contains foreign matter is supplied to the chamber and foreign matter gets in between the vane and the opposed wall in the above mentioned maximum advanced or retarded condition, it is not able to exactly obtain the maximum advanced or retarded condition. As a result, it is impossible to exactly control the valve timing with that device. Further, if the foreign matter gets in between the top end portion of the vane and an outer circumferential wall of the chamber, the fluid-tightness between the first pressure chamber and the second pressure chamber deteriorates. This causes a decrease in the response of the valve timing control device.